I have the Kenny Brown and am happy with it. I went with it mostly for access to the back seat as I still have young ones that ride back there. A NHRA legal cage has to have a horizontal bar behind the seats making getting into the back seat a bit of a chalenge, especially with a convertable.
The way I looked at it was, any roll bar is better than none. It stiffened the car and I have at least a little more peace of mind that it's safer... and the kids can get in and out without me having to put the top down!
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'92 GT conv.
TFS heads, GT40, Powerdyne 9#, AOD, 3.73
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